1. Field of the Invention
The present invention relates to a solid-solution semiconductor laser element material consisting of a solid-solution semiconductor having the general chemical formulae Pb.sub.1-x Ca.sub.x X, where 0&lt;x.ltoreq.0.5 and X is S or Se, and Pb.sub.1-x (Ca.sub.1-y Y.sub.y).sub.x X, where 0&lt;x.ltoreq.0.5, 0&lt;y&lt;1, and Y is Sr or Ba, which oscillates within a wide infrared region of wavelength of 0.4-8 .mu.m, and is operable in the vicinity of room temperature. The present invention also relates to a laser element which uses this material.
An object of the present invention is to provide a solid solution semiconductor laser element material which can produce a laser element oscillating within an infrared region of wavelength of 0.4-8 .mu.m, varying the wavelength and operating in the vicinity of a room temperature, particularly a laser element having a lattice matching type double hetero-structure or lattice matching type quantum well structure.
2. Description of the Prior Art
The structure of a semiconductor laser element is explained by referring to FIG. 1. FIGS. 1(A), 1(B) and 1(C) show a lattice matching type double hetero-structure laser element and a lattice matching type quantum well structure laser element, respectively, wherein a laser beam is emitted from an active layer 2 sandwiched by cladding layers 1, 1 in an arrow direction by flowing a current through electrodes 3.
In case of the semiconductor laser element, a laser beam is only faintly different from that of gas lasers, so that recent attempts have been made to increase luminous efficiency of a laser by using a complicated structure which divides an active layer into a barrier layer 4 and a quantum well 5 as shown in FIG. 1(C).
As a task required for the above-described semiconductor laser, it is important to increase an operating temperature and to have a good junction between a cladding layer and an active layer.
Known materials as an active layer and a cladding layer of a semiconductor laser element emitting laser beams with variable wavelength within an infrared region of wavelength of 0.4-8 .mu.m are Hg.sub.1-a Cd.sub.a Te, where 0&lt;a.ltoreq.1, as a II-VI group compound semiconductor, InAs or InSb as a III-V group compound semiconductor and each kind of IV-VI group compound semiconductors.
From the view points of high operating temperature and the degree of wavelength variability, the IV-VI group compound semiconductor is noted as the most highly usable material in the above semiconductors, and there have hitherto been known Pb.sub.1-a Cd.sub.a S.sub.1-b Se.sub.b or Pb.sub.1-a Eu.sub.a Te.sub.1-b Se.sub.b and the like as a quaternary lead salt solid solution semiconductor.
A laser element is formed by making a cladding layer of Pb.sub.1-a Cd.sub.a S.sub.1-b Se.sub.b or Pb.sub.1-a Eu.sub.a Se.sub.b Te.sub.1-b by double hetero-structure substantially coincide with the charge carrier and the lattice constant of the cladding layer and the active layer wherein an active layer is formed by one element selected from the group consisting of PbS and Pb.sub.1-a Eu.sub.a Se.sub.b Te.sub.1-b. Operating temperatures are 200 and 241 K, respectively, but are attained by pulse oscillation, and they have a further shortcoming which is lowered by continuous oscillation and these cannot practically be used.
In general, in order to increase an operating temperature of the above-described injection-type semiconductor laser, it is desired that a laser element is formed by lattice matching type double hetero-structure or lattice-matching type quantum well structure coincide with each lattice constant of charge carrier and cladding layer and active layer, and that an energy gap of the cladding layer is larger than that of the active layer and its difference is sufficiently large. However, in either one of Pb.sub.1-a Cd.sub.a S.sub.1-b Se.sub.b or Pb.sub.1-a Eu.sub.a Se.sub.b Te.sub.1-b, its difference is small, so that the low operating temperature is disadvantageous.
In the case of forming a laser element by lattice-matching type double hetero-structure or lattice-matching type quantum well structure, it is necessary to form a laser element by jointing materials having a larger energy gap of a cladding layer than that of an active layer, their large difference and substantially equal crystalline structures and lattice constants. In a general chemical formula of Pb.sub.1-a Cd.sub.a S.sub.1-b Se.sub.b or Pb.sub.1-a Eu.sub.a Se.sub.b Te.sub.1-b of a quarternary solid solution having a rock salt type crystalline structure, materials having different energy gaps and substantially equal lattice constants are obtained by separately controlling the composition (a) of an element of Cd or Eu and the composition (b) of an element of Se, so that it is possible to form a laser element by joining them.
However, in the case of actually manufacturing a laser element, a large amount of solid solution of Pb series cannot be expected from the limitation such as manufacturing condition and the like, and a quarternary solid solution is manufactured by a very small amount of solid solution at present. The above-described materials pulse-oscillated at 200 K and 241 K is understood that the compositions (a) of Cd and Eu in the above quarternary solid solution are 0.05 and 0.018, respectively, and a solid solution rate to Pb is small. Therefore, in case of producing them as a beam cladding layer, a difference between energy gaps of a cladding layer and an active layer is very small such as 0.18 (eV) at 300 K at most, 0.094 (eV) at 241 K, and a laser element having a high operating temperature cannot be obtained.
The demand for a highly efficient laser element has recently been increased, and it is particularly important to develop a solid solution semiconductor laser element operable in the vicinity of room temperature. That is, in order to increase an operating temperature of a semiconductor laser, it is an urgent task to obtain a novel solid solution semiconductor having a larger energy gap of a cladding layer than that of an active layer and a sufficiently large difference therebetween.